Project 4 - Biomedical Project 2 ? BP2 - Project Summary Native American communities in the Southwestern United States have concerns that uranium (U) and arsenic (As) exposures arising from abandoned U mine sites have increased the prevalence of metal-associated diseases including immune dysfunction. These concerns are based on environmental exposures linked to the >1100 abandoned Cold War U waste sites and documented U and As well water contamination. Immature pre- T (thymus) and pre-B (bone marrow) have been found to be extremely sensitive to As(III) and perhaps U[VI] in the form of uranyl acetate (UA) exposures. The immunotoxicity of UA has not been previously characterized. We provide preliminary data that UA interacts with As(III) to produce immunotoxicity via both genotoxic (DNA damage through PARP inhibition), and non-genotoxic (IL-7 signaling in pre-T and pre-B cells) in the mouse. We also hypothesize that immature lymphoid cells lack the ability to export metals, leading to increased exposures. In the present studies we will test this hypothesis by direct measurement of lymphoid organ concentrations following UA and As(III) exposures, alone and in combination, following drinking water exposures. It is important to understand the mechanisms of pre-T and pre-B sensitivity to UA and AsIII exposures because these pathways could explain alterations in T and B cell selection that are responsible for human immune dysregulation (such as autoimmunity), These studies provide a strong framework for interaction with BP-1 and EP-1. At the molecular level, UA and As(III) have been found to displace Zn, and inhibit PARP-1 function leading to DNA damage. Although the UA may not have strong immunotoxicity on its own, there appears to be important synergy with UA and As(III). The bases for these interactions are not well understood. The proposed studies will evaluate several potential mechanism for UA and As(III) interactions. We also propose to investigate other environmentally relevant metal mixtures. These studies also provide a framework for understanding how interventions, such as Zn supplementation, can be used to prevent arsenic/uranium toxicity (BP-1) and perhaps other environmentally relevant metal mixtures (EP-1). The proposed studies will provide critical mechanistic insights into the potential immunotoxicity of UA, its interactions with As(III) as well as other metals and, importantly, the potential for use of zinc therapy to modify immune diseases in sensitive populations who are environmentally exposed to these metals.